Many variations of patches have been used for applying medication topically, either for local or systematic effect. For example, U.S. Pat. No. 5,536,263 describes a non-occlusive medication patch to be applied to the skin including a porous self-supporting backing layer and a flexible hydrophilic pressure-sensitive adhesive reservoir comprising a hydrocolloid for sustained release of medication to be absorbed topically through the skin. U.S. Pat. No. 5,536,263 teaches that the porosity of the backing layer is important because it provides openings for receiving the medication-containing hydrocolloid reservoir and helps to assure that the patch is non-occlusive. Further, the infusion of the hydrocolloid medication-containing reservoir into the backing sheet is accomplished by controlling manufacturing parameters to keep the hydrocolloid sufficiently fluid to penetrate the backing sheet despite its tendency to thicken rapidly when applied. In order to prevent the hydrocolloid from becoming too viscous to penetrate the backing sheet, the device which applies the hydrocolloid is chilled to remove heat and to keep the hydrocolloid cool. Therefore, U.S. Pat. No. 5,536,263 teaches cooling an application device to lower viscosity of a medication-containing hydrocolloid within the device.
U.S. Pat. No. 5,635,201 discloses a method and apparatus for manufacturing a wound dressing. The method includes coating an upper surface of a perforated carrier material with a curable silicone mixture, blowing cold air onto the underside of the carrier material, and applying heat to the silicone mixture until it is cured to a silicone gel. The cold air is applied by an air blowing unit to remove an applied silicone mixture from perforations in the carrier material, thereby maintaining the porosity of the wound dressing. The cold air further prevents the silicone mixture from curing before it has time to spread over the carrier material. Thus , U.S. Pat. No. 5,635,201 teaches cooling a silicone mixture applied to a carrier strip to prevent curing of the silicone mixture.
One problem that occurs when manufacturing patches, and in particular non-occlusive patches, is undesired spreading of medication-containing ointment when the ointment is heated to a low viscosity for application to a porous backing sheet of a patch. Ointments are not water/solid emulsions and therefore have different properties than a hydrogel and react in a different manner than a hydrogel when heated and cooled. The term "ointment" as used in this application is used in a conventional sense in pharmacy and refers to a material that is semi-solid at room temperatures and softens, but not necessarily melts, at higher temperatures (e.g., when applied to the skin). The term medication is used in the sense of any bioactive agent.
Since an applied ointment fills the pores of a porous backing sheet in the area over which it is spread, the greater the surface area covered by the ointment, the less porous the backing sheet. A less porous backing sheet is undesirable because it makes the patch more occlusive and allows less moisture evaporation from the patient's skin. Lessening moisture evaporation can cause accumulation of water and could cause the patch to fall off. In addition, accumulation of water could cause the growth of bacteria beneath the patch and patient discomfort.
Increased heating of the medication-containing ointment lowers the viscosity of the ointment and thereby increases flow rate of the ointment through an ointment dispenser. Increased flow rate through the ointment dispenser can allow increased production speed and therefore a greater patch yield. However, increased heating of the ointment also increases undesired spreading of the ointment and decreases porosity as described above.
The problems identified above are not intended to be exhaustive but are among the many that reduce the effectiveness of current solutions to the problem of applying medication-containing ointment to a porous backing layer without decreasing porosity of the porous backing layer beyond a desired level; however, the problems presented above should be sufficient to demonstrate that currently known solutions are amenable to worthwhile improvement.